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Thu, 23 Jul 2020 17:55:40 +0000 (UTC) Date: Thu, 23 Jul 2020 18:55:38 +0100 From: "Dr. David Alan Gilbert" To: Stefan Hajnoczi Subject: Re: [PATCH for-5.1 2/3] virtiofsd: add container-friendly -o chroot sandboxing option Message-ID: <20200723175538.GW2621@work-vm> References: <20200722130206.224898-1-stefanha@redhat.com> <20200722130206.224898-3-stefanha@redhat.com> <20200722190318.GM2660@work-vm> <20200723123229.GK186372@stefanha-x1.localdomain> MIME-Version: 1.0 In-Reply-To: <20200723123229.GK186372@stefanha-x1.localdomain> User-Agent: Mutt/1.14.5 (2020-06-23) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Received-SPF: pass client-ip=207.211.31.120; envelope-from=dgilbert@redhat.com; helo=us-smtp-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/07/22 22:13:02 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -30 X-Spam_score: -3.1 X-Spam_bar: --- X-Spam_report: (-3.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H4=-0.01, RCVD_IN_MSPIKE_WL=-0.01, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: virtio-fs@redhat.com, rmohr@redhat.com, qemu-devel@nongnu.org, vromanso@redhat.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" * Stefan Hajnoczi (stefanha@redhat.com) wrote: > On Wed, Jul 22, 2020 at 08:03:18PM +0100, Dr. David Alan Gilbert wrote: > > * Stefan Hajnoczi (stefanha@redhat.com) wrote: > > > + /* > > > + * Make the shared directory the file system root so that FUSE_OPEN > > > + * (lo_open()) cannot escape the shared directory by opening a symlink. > > > + * > > > + * It's still possible to escape the chroot via lo->proc_self_fd but that > > > + * requires gaining control of the process first. > > > + */ > > > + if (chroot(lo->source) != 0) { > > > + fuse_log(FUSE_LOG_ERR, "chroot(\"%s\"): %m\n", lo->source); > > > + exit(1); > > > + } > > > > I'm seeing suggestions that you should drop CAP_SYS_CHROOT after > > chroot'ing to stop an old escape (where you create another jail inside > > the jail and the kernel then lets you walk outside of the old one). > > That's already the case: > > 1. setup_seccomp() blocks further chroot(2) calls. > 2. setup_capabilities() drops CAP_SYS_CHROOT. Ah yes; could you add a comment if you respin; it's not obvious that the capability to chroot allows you to break out of an existing chroot you're in. Dave > Stefan -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK